Hector, the smoke ring is a chemical reaction, it really doesn't have much to do with smoke. I suggest you take your cook from the fridge to the grill, spritzing occasionally if a pink ring is your goal. To me, if they taste good, it's a success.
Tony, typically, I'm not a foiler, but if the slab is decidedly different from one end to the other, foiling may be the answer. 6 1/2 hrs at 250° seems a bit long, but you're the one doing it, so use your instincts, and let us know your results! Fyi, beef ribs are an Achilles heel of mine.
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